Chemical vapor deposition (CVD) systems are used to form a thin, uniform layer or film on a substrate such as a semiconductor wafer. During CVD processing, the substrate is exposed to one or more chemical vapors such as silane, phosphane, diborane and the like, and gaseous substances such as oxygen. The gases mix and interact with the other gases and/or the surface of the substrate to produce the desired film. The desired reactions generally occur at elevated temperatures, for example 300.degree. C. to 500.degree. C., with the substrate and chamber being heated to the appropriate temperature for a selected process. In many applications including semiconductor processing, film characteristics such as purity and thickness uniformity must meet high quality standards.
In general, CVD systems include an injector positioned to inject chemical reagents and other gaseous substances into a clean, isolated reaction chamber. For processing occurring at atmospheric pressure, the substrate may be carried through the chamber on a conveyor or positioned on a stationary support. Vents are positioned on opposite sides of the injector body to remove waste products such as unused reagents and reaction by-products from the reaction chamber. Removing unreacted gases and particulate contamination is necessary to maintain the clean environment of the reaction chamber as well as prevent these materials from being incorporated into the films deposited on the surface of the substrate during processing. The exhaust flows upwardly through the vents and is removed by a reduced pressure exhaust system.
The CVD system typically includes a vent assembly coupled to an exhaust system for removing waste products such as unreacted gases and powders formed during the reaction from the chamber. Removing unreacted gases and particulate contamination is necessary to maintain the clean environment of the reaction chamber as well as prevent these materials from being incorporated into the films deposited on the surface of the substrate during processing. The reaction chamber and vent assembly must be periodically cleaned to eliminate sources of particulate contamination which may become embedded in the film. Typically, cleaning of the vent system may be required as often as every twenty hours of operation to prevent particles from falling on the films during processing, requiring frequent interruption of the CVD process.
As is shown in FIGS. 1A and 1B, the vent assembly which is typically used with elongate, linear injectors include an elongate, vertical vent 1 having a tapered upper end 2 formed with an outlet 3. The outlet 3 is coupled to the low pressure exhaust system for disposal of the waste by-products of the reaction. Although this vent assembly may be used to remove the majority of reaction by-products from the chamber, particles are deposited on the inner surfaces of the vent by the waste materials requiring that the vent assembly be frequently removed and cleaned.
A vent assembly which may be used for extended periods of time without requiring interruption of the CVD process for cleaning, maintenance or replacement is desirable. In addition, a vent assembly which minimizes the risk of particles collecting in the vent assembly and then falling into the reaction chamber is desired. A vent assembly with improved efficiency in delivering particles and unreacted gases from the vent assembly to the exhaust system, minimizing the amount of particulate matter collecting in the vent assembly, is also desirable.